Pictures reveal a cosmic 'beast'

Research out today links black holes to one of the universe's most

By
Robert C. Cowen, Special to The Christian Science Monitor /
October 28, 1999

BOSTON

After decades of hunting, astronomers are closing in on the "beast" that lurks behind some of the most powerful forces in the universe. That's the name they give to the invisible energy source that shoots jets of particles at nearly the speed of light from the cores of so-called active galaxies.

A global array of radio telescopes finally has revealed details of what's going on at the edge of the lair of one of these beasts, a region astronomers had previously considered almost impossible to penetrate.

Now, these images, along with images released earlier this week of a different jet, provide strong new evidence that massive black holes are powering these phenomena. Indeed, they offer further insight into one of the least-understood mechanisms of the cosmos.

In black holes, a mass billions of times the mass of the sun is crammed into a volume no larger than our solar system. The gravity of this concentration is so powerful that nothing falling into it, including light, can escape.

Yet some of the matter attracted to the black hole does not fall in. It is deflected to form a disk. Black-hole theory predicts that electrical and magnetic forces in this rapidly spinning disk can accelerate electrically charged particles to high speeds and spew them out as jets.

William Junor at the University of New Mexico in Albuquerque and John Biretta and Mario Livio at the Space Telescope Science Institute in Baltimore say that the radio image they have published in Nature today supports this theory.

The data are consistent with a disk threaded by magnetic fields surrounding a central black hole that is 3 billion times as massive as the sun.

They show particles accelerating out from the region of the suspected disk in Virgo A galaxy, which is 50 million light-years from Earth. The particle streams then pinch down to form a tightly collimated jet.

"We're getting close to the black hole [itself]," Dr. Junor says when asked about the significance of the team's findings. He adds that "there has to be some global influence" guiding the jets. Magnetic fields probably are involved in that.

Meanwhile, an image from the new Chandra orbiting X-ray telescope has added to this picture. It has imaged one of the most spectacular galactic jets in unprecedented detail.

This jet erupts from the core of the Centaurus A galaxy, 11 million light-years away from Earth. It shoots out for 25,000 light-years. That's a distance comparable to the diameter of our own Milky Way galaxy.

The image, which NASA released Monday, shows that the X-rays seen from the Centaurus A jet are coming from electrons spiraling around a magnetic field.

What is equally intriguing, the image shows previously unobserved X-ray sources clustered around the galaxy core.

Christine Jones at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., notes that these sources "are grouped in a sphere around the nucleus, which must be telling us something very fundamental about how the galaxy, and the supermassive black hole in the center, were formed."

Such discoveries are the beginning of a new phase in this research, in which the ability to see fine detail may finally reveal the true nature of the power source of active galaxies - which throw out massive amounts of energy at many wavelengths.

For example, in studying Virgo A, astronomers used the continent-wide Very Long Baseline Array radio telescope system across North America, as well as another radio telescope array near Socorro in New Mexico.

They also used radio telescopes in Finland, Germany, Italy, Spain, and Sweden.

The combined signals from all these telescopes acted, in effect, as one large telescope with the diameter of Earth. Since a telescope's ability to resolve detail depends on its diameter, this gave astronomers unprecedented image sharpness.

Also, since both Virgo A and Centaurus A are close by, astronomers can combine the detailed X-ray and radio data with increasingly precise data from visible and infrared light telescopes and gamma-ray satellites. This lets astronomers track the black-hole "beast" with every weapon in their arsenal.